Jackneck
A Jackneck is a person who talks nonsense and gets the worst punishment for it.
Jackneck: "I'm gonna be a rockstar." Me: "You're gonna be a nobody."
Jackneck: "I'm gonna win this." Me: "You're gonna lose like a loser."
Jackneck: "You're the worst." Me: "You're the one who got kicked out of class."